It is well known to place materials within packages, such as plastic packages or packages comprising resinous materials, and sealing the material therein using heat. For example, liquid or semi-liquid materials are typically placed in a pliable package, such as between two leak-proof resinous sheets which are subsequently sealed together at the edges using electromagnetic radiation. One problem encountered with such packages is that the contained material can spread and contaminate the seal area prior to sealing. As a result, during the sealing process the material becomes entrapped within the seal, reducing the effectiveness of the seal. Problems resulting from such contaminated seals are well known in the art. For example, contaminants within the sealed area can prevent the resinous sheets from sealing together, causing a weakness in the seal. Additionally, in applications where appearance is important, the contaminants in the seal area can be unsightly. Furthermore, if the area of contamination is large enough to compromise the seal, material can leak out of the package.
U.S. Pat. No. 4,117,306 by Shah issued Sept. 26, 1978, discloses a device for enabling the detection of contaminants within a sealed area. This device includes a grooved, heated sealing bar and a grooved anvil, which together produce a corrugated seal. The corrugated seal provides for the visible detection of contamination in a seal area. However, this device only permits detection of the contamination, it does not reduce or eliminate the problem of contamination.
U.S. Pat. No. 3,851,444 by Merat issued Dec. 3, 1974, discloses a device for keeping air borne contaminants, such as dust or powder, away from a seal area. This mechanical device protects the seal area during the filling of a package and is then removed. This provides a clean area for sealing. However, there is no disclosure of a method for removing contaminants from the seal area after filling and prior to sealing.
A particular type of materials which are typically sealed within a package are flowable, pressure-compensating materials. A common use for such materials is in padding devices. In use, the flowable, pressure-compensating materials are typically placed in a pliable package, such as between two leak-proof resinous sheets which are sealed at the edges. The flowable materials act hydraulically. An applied force causes flowable, pressure-compensating material to migrate from areas of higher pressure to areas of lower pressure until pressure throughout the package is uniform. Once conformity has been achieved, force is distributed substantially equally over the entire surface of the package thus alleviating the differential pressure problems associated with prior devices. Flowable, pressure-compensating materials are presently marketed under the trademark FLOLITE.TM. by Alden Laboratories, Inc. of Boulder, Colo. U.S.A.
In order to function properly, the flowable, pressure-compensating materials must occupy all, or substantially all of the volume of the package in which they are contained. In this way, when pressure is applied to a package which contains flowable, pressure-compensating material, the material may flow to conform to the shape of the pressure applying object, but its flow is restrained by the volume of the package. Therefore, the material can support and distribute the force of the pressure applying object. However, during the production of such padding devices, it is often difficult to remove excess air from the unsealed package prior to sealing without contaminating the seal area with the material.
Various padding devices which do not employ flowable, pressure-compensating material are generally available. Examples include liquid- or gas-filled bladders, e.g. water-filled cushions and pneumatic pads; and gases or liquids dispersed in a solid material, e.g. foams and gels. Generally, such padding devices operate on the principle of conformation to the shape of an object when placed under pressure. When a force, such as a person's mass, is placed on such a padding device, the device deforms so as to conform to the shape of the pressure applying object in order to distribute the force over as large an area as possible. These devices perform adequately when the object being padded has a relatively large, uniformly shaped surface area. However, when the object being padded includes a relatively small area of concentrated force, such as that caused by a protuberance, the majority of known padding devices do not perform to adequately reduce the discomfort of users in many applications. This is because many padding devices exert greater responsive pressure on the area of concentrated force.
The problem can be described with reference to a padding device comprising a gas dispersed in a solid material, e.g. foam. Tiny gas bubbles in foam act like millions of coil "springs." When required to conform to an irregular shape, such as a human body, the "springs" are compressed to varying degrees, each pushing back on the body with a force proportional to the amount of compression. Intimate conformity is best obtained with a relatively soft foam, which can be compared to weak "springs." The pressure on protuberances, where the "springs" are greatly compressed, will be relatively high, possibly causing pain and reduced circulation. The problem is even more pronounced if a stiffer foam is employed, because the "springs" are stronger.
In order to alleviate the problem of differential pressure inherent with many prior art materials, flowable, pressure-compensating materials were developed. Such materials and applications thereof are described in U.S. Pat. No. 3,402,411 by Alden Hanson, issued Sept. 24, 1968; U.S. Pat. No. 3,635,849 by Alden Hanson, issued Jan. 18, 1972; U.S. Pat. No. 4,038,762 by Swan, Jr., issued Aug. 2, 1977; U.S. Pat. No. 4,083,127 by Chris Hanson, issued Apr. 11, 1978; U.S. Pat. No. 4,108,928 by Swan, Jr., issued Aug. 22, 1978; U.S. Pat. No. 4,144,658 by Swan, Jr., issued Mar. 20, 1979; U.S. Pat. No. 4,229,546 by Swan, Jr., issued Oct. 21, 1980; and U.S. Pat. No. 4,243,754 by Swan, Jr., issued Jan. 6, 1981. As used herein, the term "flowable, pressure-compensating materials" will include the materials disclosed in these patents. Each of these U.S. patents is incorporated herein by reference in its entirety. These patents will collectively be referred to as the "flowable, pressure-compensating material patents."
The preferred materials disclosed in U.S. Pat. No. 3,402,411 comprise 20 to 25 weight percent polyisobutylene, 25 to 37.5 weight percent of an inert oil, e.g. mineral oil or a saturated ester oil or a mixture thereof and 42.5 to 50 weight percent inorganic filler. U.S. Pat. No. 3,635,849 discloses a composition consisting essentially of from about 5 to about 45 weight percent of a polyolefin, particularly polyisobutylene, from about 15 to about 70 weight percent of a paraffin and from about 5 to about 80 weight percent oil. Lightweight aggregate materials, for example, polystyrene beads or a heavy aggregate such as Fe.sub.3 O.sub.4 can also be added.
The flowable, pressure-compensating materials disclosed in U.S. Pat. Nos. 4,038,762, 4,108,928 and 4,243,754 include from 21.39 to 77.96 weight percent oil, 21.04 to 69.62 weight percent wax and 1 to 9 weight percent microbeads. The inclusion of water in the compositions disclosed in these patents is discouraged. It is disclosed that because water generally increases the specific gravity of the finished fitting material, and does not serve any functional or necessary purpose in the finished fitting material, it is very desirable that if it is present in the finished fitting material, that it not be present in amounts or levels that exceed tolerable, minimal or residual levels (e.g. up to or not exceeding 8 weight percent, preferably up to or not exceeding 3 or 5 weight percent).
U.S. Pat. Nos. 4,144,658 and 4,229,546 disclose flowable, pressure-compensating materials comprising 10 to 60 weight percent hollow, glass microbeads, 8.5 to 34 weight percent wax and 26.5 to 81 weight percent oil. U.S. Pat. No. 4,083,127 discloses a flowable, pressure-compensating fitting material consisting essentially of discrete, lightweight, sturdy microbeads distributed throughout a continuous phase of wax and oil.
The materials described in the flowable, pressure-compensating material patents represent an advance in the art in terms of force distribution and stability. The materials distribute forces better than foams and gels because the force is evenly distributed, irrespective of the shape of the force applying object. Additionally, they represent advances in terms of responsiveness when compared to less viscous fluids such as water-filled devices. Logically, it would appear that water would be an excellent cushioning material because of its capability to almost instantaneously flow to achieve conformability. However, incompressible materials which provide almost instantaneous conformability do not provide as much control and stability as flowable, pressure-compensating materials, which do not respond to instantaneously applied pressure. Anyone who has attempted to sit on a waterbed is familiar with the lack of stability associated with water-cushioned devices. However, in spite of the advantages which flowable, pressure-compensating materials have over prior art padding materials, there could still be improvement in the compositions with respect to problems caused by contaminated seals.
Therefore, it would be advantageous to provide a method which reduces or eliminates the problem of contaminated seals. It would be advantageous if such a method were simple and easy to perform. It would also be advantageous if the method could be performed on seals which have been contaminated with flowable, pressure-compensating materials. In particular, it would be advantageous to provide a method for heat sealing a flowable, pressure-compensating material within a resinous package while simultaneously reducing the amount of excess air within the package and reducing the problems associated with contaminated seals. Additionally, it would be advantageous if a composition usable in such a method could be provided.